Lewis Acid Stabilized OPI3: Implications for the Nature of Free OPI3
While reinvestigating the published synthesis of OPI3, it became evident from the experiments that phosphoryl triodide may only be formed as an intermediate and that the end products of the reaction of OPCl3 with LiI are PV oxides, PI3, I2, and LiCl. This is also in agreement with MP2/TZVPP calculations, which assign DeltarH° (DeltarG°) [DeltarG° in CHCl3] for the disproportionation of OPI3 as -7 (-18) [-17 kJ mol-1] (assuming P4O10 as the PV oxide). The first products of this reaction visible in a low-temperature in situ 31P NMR experiment are P2I4 and PI3, as well as traces of a compound that may be OPCl2I. By contrast, it was possible to prepare and structurally characterize Lewis acid [A] stabilized [A]OPX3 adducts, where [A] is Al(ORF)3 for X=Br and Al(ORF)2(-F)Al(ORF)3 for X=I (RF=C(CF3)3). These adducts are formed on decomposition of PX4+[Al(ORF)4]-; high yields of Br3POAl(ORF)3 (delta(31P)=-65) were obtained, while I3POAl(ORF)3 (delta(31P)=-337) and I3POAl(ORF)2(-F)Al(ORF)3 (delta(31P)=-332) are only formed as by-products. The main product of the room-temperature decomposition of PI4+[Al(ORF)4]- is PI4+[(RFO)3Al(-F)Al(ORF)3]-, which was also characterized by X-ray crystallography and was independently prepared from Ag+[(RFO)3Al(-F)Al(ORF)3]-, PI3, and I2.